The present invention relates to a tube mill for forming tubular stock from flat roll stock, more particularly, to a tube mill which forms a perforated tube from flat roll stock fed to the mill in an imperforate condition. It is also concerned with a particular perforated tube configuration wherein protrusions are formed in association with the perforations to alter the path of fluid flowing through the tube.
The flat roll stock supplied to tube mills of the type with which the present invention is concerned is typically supplied to the mill in a coil. In processing, the stock is drawn from the coil directly into the mill. Prior art techniques wherein such stock was used for forming perforated tubes have relied upon a discontinuous operation wherein the strip is first uncoiled and passed through a punch press, then recoiled and, ultimately, again uncoiled as it is drawn through the tube mill.
The prior art also discloses the use of roll presses to perforate sheet stock which is, ultimately, formed into a tube. U.S. Pat. Nos. 1,053,614 and 1,849,188 disclose such roll presses. These patents do not, however, suggest the concept of incorporating a roll press into a tube mill so as to direct the output of the press directly into the mill, without the necessity of recoiling the flat roll stock. The die and press rolls of the roll presses disclosed in these patents incorporate complementally interengagable elements which necessitate synchronized drive of the rolls.
U.S. Pat. No. 3,858,785 is of interest with respect to the present invention in that it discloses a tube mill wherein strip patterning rolls are disposed at the lead end of the mill to pattern the surface of flat roll stock fed through the mill. This patent does not, however, suggest the incorporation of a perforating roll press into a tube mill, nor the design of a tube mill to accommodate perforated stock processed by such a mill.
The prior art also suggests that mufflers for internal combustion engines may be provided with tubular core elements having perforations therein with protruding edges. U.S. Pat. Nos. 3,276,108 and 3,286,786 are examples of such art.